The LM555/NE555/SA555 is a highly stable timer capable of producing accurate timing pulses from microseconds to hours. It has a monostable operation where the time delay is controlled by one external resistor and capacitor. It also has an astable operation where the frequency and duty cycle are accurately controlled by two external resistors and one capacitor. The timer has high current drive capability, adjustable duty cycle, and temperature stability of 0.005%/°C.

1. www.fairchildsemi.com
LM555/NE555/SA555
Single Timer
Features Description
• High Current Drive Capability (200mA) The LM555/NE555/SA555 is a highly stable controller
• Adjustable Duty Cycle capable of producing accurate timing pulses. With a
• Temperature Stability of 0.005%/°C monostable operation, the time delay is controlled by one
• Timing From µSec to Hours external resistor and one capacitor. With an astable
• Turn off Time Less Than 2µSec operation, the frequency and duty cycle are accurately
controlled by two external resistors and one capacitor.
Applications
8-DIP
• Precision Timing
• Pulse Generation
• Time Delay Generation 1
• Sequential Timing
8-SOP
1
Internal Block Diagram
R R R
GND 1 8 Vcc
Comp. Discharging Tr.
Trigger 2 7 Discharge
OutPut
Output 3
Stage F/F 6 Threshold
Comp.
Control
Reset 4 5
Vref Voltage
Rev. 1.0.3
©2002 Fairchild Semiconductor Corporation

2. LM555/NE555/SA555
Absolute Maximum Ratings (TA = 25°C)
25°
Parameter Symbol Value Unit
Supply Voltage VCC 16 V
Lead Temperature (Soldering 10sec) TLEAD 300 °C
Power Dissipation PD 600 mW
Operating Temperature Range
LM555/NE555 TOPR 0 ~ +70 °C
SA555 -40 ~ +85
Storage Temperature Range TSTG -65 ~ +150 °C
2

3. LM555/NE555/SA555
Electrical Characteristics
(TA = 25°C, VCC = 5 ~ 15V, unless otherwise specified)
Parameter Symbol Conditions Min. Typ. Max. Unit
Supply Voltage VCC - 4.5 - 16 V
VCC = 5V, RL = ∞ - 3 6 mA
Supply Current (Low Stable) (Note1) ICC
VCC = 15V, RL = ∞ - 7.5 15 mA
Timing Error (Monostable)
Initial Accuracy (Note2)
ACCUR - 1.0 3.0 %
Drift with Temperature (Note4) RA = 1kΩ to100kΩ
∆t/∆T 50 ppm/°C
Drift with Supply Voltage (Note4) C = 0.1µF
∆t/∆VCC 0.1 0.5 %/V
Timing Error (Astable)
-
Intial Accuracy (Note2) ACCUR RA = 1kΩ to 100kΩ 2.25 - %
Drift with Temperature (Note4) ∆t/∆T C = 0.1µF 150 ppm/°C
Drift with Supply Voltage (Note4) ∆t/∆VCC 0.3 %/V
VCC = 15V 9.0 10.0 11.0 V
Control Voltage VC
VCC = 5V 2.6 3.33 4.0 V
VCC = 15V - 10.0 - V
Threshold Voltage VTH
VCC = 5V - 3.33 - V
Threshold Current (Note3) ITH - - 0.1 0.25 µA
VCC = 5V 1.1 1.67 2.2 V
Trigger Voltage VTR
VCC = 15V 4.5 5 5.6 V
Trigger Current ITR VTR = 0V 0.01 2.0 µA
Reset Voltage VRST - 0.4 0.7 1.0 V
Reset Current IRST - 0.1 0.4 mA
VCC = 15V
ISINK = 10mA - 0.06 0.25 V
Low Output Voltage VOL ISINK = 50mA 0.3 0.75 V
VCC = 5V
- 0.05 0.35 V
ISINK = 5mA
VCC = 15V
ISOURCE = 200mA 12.5 - V
High Output Voltage VOH ISOURCE = 100mA 12.75 13.3 V
VCC = 5V
2.75 3.3 - V
ISOURCE = 100mA
Rise Time of Output (Note4) tR - - 100 - ns
Fall Time of Output (Note4) tF - - 100 - ns
Discharge Leakage Current ILKG - - 20 100 nA
Notes:
1. When the output is high, the supply current is typically 1mA less than at VCC = 5V.
2. Tested at VCC = 5.0V and VCC = 15V.
3. This will determine the maximum value of RA + RB for 15V operation, the max. total R = 20MΩ, and for 5V operation, the max.
total R = 6.7MΩ.
4. These parameters, although guaranteed, are not 100% tested in production.
3

4. LM555/NE555/SA555
Application Information
Table 1 below is the basic operating table of 555 timer:
Table 1. Basic Operating Table
Threshold Voltage Trigger Voltage Discharging Tr.
Reset(PIN 4) Output(PIN 3)
(Vth)(PIN 6) (Vtr)(PIN 2) (PIN 7)
Don't care Don't care Low Low ON
Vth > 2Vcc / 3 Vth > 2Vcc / 3 High Low ON
Vcc / 3 < Vth < 2 Vcc / 3 Vcc / 3 < Vth < 2 Vcc / 3 High - -
Vth < Vcc / 3 Vth < Vcc / 3 High High OFF
When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or
the trigger voltage. Only when the high signal is applied to the reset terminal, the timer's output changes according to
threshold voltage and trigger voltage.
When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal discharge Tr.
turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained
low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal
discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high.
1. Monostable Operation
+Vcc
2
10
4 8 RA
RESET Vcc 10
1
kΩ
Ω
Trigger
Ω
kΩ
DISCH 7
Ω
=1
M
0k
10
1M
10
10
A
A
R
2
Capacitance(uF)
TRIG 10
0
THRES 6
-1
10
3 OUT C1
CONT 5 -2
10
GND
RL 1 C2
-3
10
-5 -4 -3 -2 -1 0 1 2
10 10 10 10 10 10 10 10
Time Delay(s)
Figure 1. Monoatable Circuit Figure 2. Resistance and Capacitance vs.
Time delay(td)
Figure 3. Waveforms of Monostable Operation
4

5. LM555/NE555/SA555
Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls
below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's
internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1
and setting the flip-flop output at the same time.
The voltage across the external capacitor C1, VC1 increases exponentially with the time constant t=RA*C and reaches 2Vcc/3
at td=1.1RA*C. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC, the longer it takes
for the VC1 to reach 2Vcc/3. In other words, the time constant RAC controls the output pulse width.
When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop,
turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low.
In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship
based on RA and C. Figure 3 shows the general waveforms during the monostable operation.
It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer
output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is
high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse
remains at below Vcc/3. Figure 4 shows such a timer output abnormality.
Figure 4. Waveforms of Monostable Operation (abnormal)
2. Astable Operation
+Vcc
100
RA (R A+2R B)
4 8 10
1k
1
Ω
RESET Vcc
10
7
Capacitance(uF)
kΩ
DISCH 1
10
2 TRIG
00
0
0
kΩ
RB
1M
1
Ω
Ω
Ω
THRES 6
Ω
0.1
10
0M
Ω
Ω
Ω
Ω
3 OUT C1 0.01
CONT 5
GND
RL 1 C2 1E-3
100m 1 10 100 1k 10k 100k
Fr equency(Hz)
Figure 5. Astable Circuit Figure 6. Capacitance and Resistance vs. Frequency
5

6. LM555/NE555/SA555
Figure 7. Waveforms of Astable Operation
An astable timer operation is achieved by adding resistor RB to Figure 1 and configuring as shown on Figure 5. In the astable
operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multi
vibrator. When the timer output is high, its internal discharging Tr. turns off and the VC1 increases by exponential
function with the time constant (RA+RB)*C.
When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high,
resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges
through the discharging channel formed by RB and the discharging Tr. When the VC1 falls below Vcc/3, the comparator
output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the
VC1 rises again.
In the above process, the section where the timer output is high is the time it takes for the VC1 to rise from Vcc/3 to 2Vcc/3,
and the section where the timer output is low is the time it takes for the VC1 to drop from 2Vcc/3 to Vcc/3. When timer output
is high, the equivalent circuit for charging capacitor C1 is as follows:
RA RB
Vcc C1 Vc1(0-)=Vcc/3
dv c1 V cc – V ( 0- )
C ------------ = ------------------------------
- - (1)
1 dt RA + RB
V ( 0+ ) = V ⁄3 (2)
C1 CC
 t 
 -  – ------------------------------------ 
( R + R )C1
 2  A B 
V C1 ( t ) = V CC  1 – -- e
-  (3)
 3 
 
Since the duration of the timer output high state(tH) is the amount of time it takes for the VC1(t) to reach 2Vcc/3,
6

7. LM555/NE555/SA555
 t 
 -  – ------------------------------------ 
H
2  2  ( R A + R B )C1 
V ( t ) = -- V
- =V  1 – -- e
-  (4)
C1 3 CC CC  3 
 
t = C ( R + R )In2 = 0.693 ( R + R )C (5)
H 1 A B A B 1
The equivalent circuit for discharging capacitor C1, when timer output is low is, as follows:
RB
C1 VC1(0-)=2Vcc/3 RD
dv 1
C1
C 1 -------------- + ---------------------- V C1 = 0
- (6)
dt R +R
A B
t
- ------------------------------------
-
2 ( R A + R D )C1
V C1 ( t ) = -- V
- (7)
3 CC e
Since the duration of the timer output low state(tL) is the amount of time it takes for the VC1(t) to reach Vcc/3,
tL
- ------------------------------------
( R A + R D )C1
-
1 2
-- V
- = -- V
- (8)
3 CC 3 CC e
t = C ( R + R )In2 = 0.693 ( R + R )C (9)
L 1 B D B D 1
Since RD is normally RB>>RD although related to the size of discharging Tr.,
tL=0.693RBC1 (10)
Consequently, if the timer operates in astable, the period is the same with
'T=tH+tL=0.693(RA+RB)C1+0.693RBC1=0.693(RA+2RB)C1' because the period is the sum of the charge time and discharge
time. And since frequency is the reciprocal of the period, the following applies.
1 1.44
frequency, f = -- = ---------------------------------------
- - ( 11 )
T ( R + 2R )C
A B 1
3. Frequency divider
By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure
8. illustrates a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.
7

8. LM555/NE555/SA555
Figure 8. Waveforms of Frequency Divider Operation
4. Pulse Width Modulation
The timer output waveform may be changed by modulating the control voltage applied to the timer's pin 5 and changing the
reference of the timer's internal comparators. Figure 9 illustrates the pulse width modulation circuit.
When the continuous trigger pulse train is applied in the monostable mode, the timer output width is modulated according to
the signal applied to the control terminal. Sine wave as well as other waveforms may be applied as a signal to the control
terminal. Figure 10 shows the example of pulse width modulation waveform.
+Vcc
RA
4 8
RESET Vcc
7
Trigger DISCH
2 TRIG
6
THRES
Output
3 OUT
Input
GND
CONT 5 C
1
Figure 9. Circuit for Pulse Width Modulation Figure 10. Waveforms of Pulse Width Modulation
5. Pulse Position Modulation
If the modulating signal is applied to the control terminal while the timer is connected for the astable operation as in Figure 11,
the timer becomes a pulse position modulator.
In the pulse position modulator, the reference of the timer's internal comparators is modulated which in turn modulates the
timer output according to the modulation signal applied to the control terminal.
Figure 12 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave
shape could be used.
8

9. LM555/NE555/SA555
+Vcc
RA
4 8
RESET Vcc
7
DISCH
2 TRIG
RB
6
THRES
Output
3 OUT
Modulation
GND
CONT 5 C
1
Figure 11. Circuit for Pulse Position Modulation Figure 12. Waveforms of pulse position modulation
6. Linear Ramp
When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the VC1
increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the
generated linear ramp waveforms.
+Vcc
RE R1
4 8
RESET Vcc
DISCH 7
2 TRIG Q1
THRES 6 R2
Output
3 OUT C1
CONT 5
GND
1 C2
Figure 13. Circuit for Linear Ramp Figure 14. Waveforms of Linear Ramp
In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and RE.
V –V
I CC E
= --------------------------
- ( 12 )
C R
E
Here, V
E is
R2
V = V + --------------------- V
- ( 13 )
E BE R 1 + R 2 CC
For example, if Vcc=15V, RE=20kΩ, R1=5kW, R2=10kΩ, and VBE=0.7V,
VE=0.7V+10V=10.7V
Ic=(15-10.7)/20k=0.215mA
9

10. LM555/NE555/SA555
When the trigger starts in a timer configured as shown in Figure 13, the current flowing through capacitor C1 becomes a
constant current generated by PNP transistor and resistors.
Hence, the VC is a linear ramp function as shown in Figure 14. The gradient S of the linear ramp function is defined as
follows:
Vp – p
S = ---------------- ( 14 )
T
Here the Vp-p is the peak-to-peak voltage.
If the electric charge amount accumulated in the capacitor is divided by the capacitance, the VC comes out as follows:
V=Q/C (15)
The above equation divided on both sides by T gives us
V Q⁄T
--- = -----------
- - ( 16 )
T C
and may be simplified into the following equation.
S=I/C (17)
In other words, the gradient of the linear ramp function appearing across the capacitor can be obtained by using the constant
current flowing through the capacitor.
If the constant current flow through the capacitor is 0.215mA and the capacitance is 0.02µF, the gradient of the ramp function
at both ends of the capacitor is S = 0.215m/0.022µ = 9.77V/ms.
10

11. LM555/NE555/SA555
Mechanical Dimensions
Package
Dimensions in millimeters
8-DIP
)
6.40 ±0.20
0.031
0.79
0.252 ±0.008
1.524 ±0.10
0.060 ±0.004
0.018 ±0.004
0.46 ±0.10
(
#1 #8
0.362 ±0.008
MAX
9.20 ±0.20
0.378
9.60
#4 #5
0.100
2.54
5.08 3.30 ±0.30
MAX 0.130 ±0.012
0.200
7.62
0.300 3.40 ±0.20 0.33
0.134 ±0.008 0.013 MIN
+0.10
0.25 –0.05
+0.004
0.010 –0.002
0~15°
11

12. LM555/NE555/SA555
Mechanical Dimensions (Continued)
Package
Dimensions in millimeters
8-SOP
0.1~0.25
MIN
0.004~0.001
1.55 ±0.20
0.061 ±0.008
)
0.022
0.56
(
#1 #8
0.194 ±0.008
MAX
4.92 ±0.20
0.202
5.13
0.016 ±0.004
0.41 ±0.10
#4 #5
0.050
1.27
6.00 ±0.30 1.80
0.236 ±0.012 MAX
0.071
0.006 -0.002
0.15 -0.05
MAX0.004
MAX0.10
3.95 ±0.20
+0.004
+0.10
0.156 ±0.008
8°
5.72
0~
0.225
0.50 ±0.20
0.020 ±0.008
12

13. LM555/NE555/SA555
Ordering Information
Product Number Package Operating Temperature
LM555CN 8-DIP
0 ~ +70°C
LM555CM 8-SOP
Product Number Package Operating Temperature
NE555N 8-DIP
0 ~ +70°C
NE555D 8-SOP
Product Number Package Operating Temperature
SA555 8-DIP
-40 ~ +85°C
SA555D 8-SOP
13

14. LM555/NE555/SA555
DISCLAIMER
FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY
PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
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OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems 2. A critical component in any component of a life support
which, (a) are intended for surgical implant into the body, device or system whose failure to perform can be
or (b) support or sustain life, and (c) whose failure to reasonably expected to cause the failure of the life support
perform when properly used in accordance with device or system, or to affect its safety or effectiveness.
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
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